Abstract:

It is necessary to carry out subclassification for tunnel surrounding rock in typical soilrock mixture backfill area in Chonging. Hence, laboratory basic physical property test is conducted to obtain the basic physical parameters of the soilrock mixture such as natural density, dry density, water content and rock content. And then laboratory largescale direct shear test and largescale triaxial test are conducted to study the variation laws of strength and deformation characteristic of soilrock mixture with water content, rock content and confining pressure. Finally, based on laboratory test results, the soilrock backfill in Chongqing is classified by taken water content and rock content as indices, and surrounding rock classification indices and method suit for soilrock mixture backfill in Chongqing area are put forward. Some conclusions are drawn as follows: (1) The soilrock mixture backfill in Chongqing belongs to poorly graded soil. (2) With the increase of water content, the cohesion and internal friction angle of soilrock mixture decrease rapidly first and then slowly. (3) With the increase of rock content, the internal friction angle of the soilrock mixture increases, and shows a "slowfastslow" pattern; while the cohesion decreases rapidly first and then slowly. (4) For the backfill of soilrock mixture in Chongqing area, the water content and rock content are priorities in key indices of surrounding rock classification. (5) The surrounding rock of soilrock mixture in Chongqing area is further subdivided into Grade Ⅳ, Ⅴa and Ⅴb, of which Grade Ⅴa and Ⅴb are slightly better Grade Ⅴ and slightly worse Grade Ⅴ respectively.

Key words: soilrock mixture, backfill, tunnel, surrounding rock classification, classification index